In a victory for climate and clean air, the Federal Highway Administration responded to a lawsuit brought by U.S. PIRG, NRDC, and the Southern Environmental Law Center on behalf of Clean Air Carolina by reinstating a federal requirement that state and local planners track and curb carbon pollution from cars and trucks on the national highways, which is a major contributor to climate change.

We brought this lawsuit after the Trump administration, without notice or opportunity for public comment, abruptly announced in May that it would “indefinitely delay” the greenhouse gas (GHG) sections of an administrative rule promulgated under the Moving Ahead for Progress in the 21st Century Act (MAP-21). The rule, which was finalized by the Obama administration in January, requires states to measure heat-trapping carbon pollution generated from vehicles traveling on the National Highway System and to set targets for reducing that pollution.

This is an important rule that will move us forward in the transition to a cleaner, healthier transportation system. And given the need for a radical transformation of our fossil fuel-powered transportation systems, every step forward is worth defending. Which is why this news was so welcome.

Transportation is the leading source of carbon pollution in the United States and our transportation sector produces more carbon pollution than the entire economies of every nation on earth save China, India and Russia. To tackle climate change we must limit pollution from our transportation system—and quickly. If we don’t, the effects, many of which we are already feeling, will be dire.

Policies to reduce greenhouse gas pollution from transportation are essential to minimize the impacts of climate change, which has been recognized by health experts worldwide as the greatest threat to global health in the 21st century. Climate change is already harming the health of Americans, particularly older adults, young children, and people with existing lung and heart problems. Rising temperatures and changing seasonal patterns have already worsened air quality in some parts of the country, and continued declines are expected to lead to more premature deaths from asthma and other respiratory and heart conditions, hospital visits, and missed work and school days. Due to the concentrated levels of greenhouse gas emissions, people who live near highly traveled roads are at increased risk of developing respiratory disease and lung cancer, and at greater risk of death from stroke, lung disease and heart disease.

The transportation system has become so bad because of our over reliance on cars and trucks that run on dirty fossil fuels like gas and diesel. In the 20th century, Americans fell in love with the car. Driving a car became a rite of passage. Owning a car became a symbol of American freedom and mobility. And so we invested in a network of interstate highways that facilitated travel and connected the nation. But we’re in a new century, and we now know that our cars harm us and the environment. We need to pursue policies that get people out of cars and encourage cleaner modes of transportation, like biking, walking, and mass transit.

In January, the Obama administration took an important step towards the goal of a cleaner, healthier transportation system by adopting the rule and requiring states to measure heat-trapping carbon pollution generated from vehicles traveling on the National Highway System and to set targets for reducing that pollution. The rule was the final in a series under the Moving Ahead for Progress in the 21st Century or MAP-21 transportation law enacted in 2012. Collectively these rules would achieve the law’s promise to launch transportation into the 21st century by making it more performance-driven. It’s a simple but profound premise: Transportation plans must be more accountable for performance outcomes, including carbon pollution. If transportation planners are required to account for carbon pollution, they will be more likely to prioritize projects that encourage cleaner modes of transportation.

We only have to look as far as California to know that this will work. California implemented a similar law nine years ago. Since then, regions across the state have spent billions improving public transportation choices such as light-rail and buses and creating new infrastructure for safe walking and biking. They have also created new innovative mobility choices such as the recently launched Ford Go Bike bikeshare system in the Bay Area, or the low-income electric carshare program in Los Angeles. The persistent theme across regions is to reduce reliance on driving by creating competitive, affordable, low-carbon transportation choices.

But before the rule could take effect, the Trump administration, without notice or opportunity for public comments, indefinitely delayed its implementation. If that sounds wrong, that’s because it is.

We sued to reverse this ill-advised and illegal action and the Trump administration has caved—at least for now. On Monday, the Federal Highway Administration (FHWA), an agency within the U.S. Department of Transportation (DOT), published a notice indicating that the rule has been reinstated and is to take effect upon publication in the Federal Register.

With the FHWA’s latest action, states are now required to engage in a process to measure—or benchmark—the carbon pollution emitted by vehicles on the national highway system to project how much it would grow in coming decades based on plans that receive federal assistance, and then set targets for reducing that pollution.

Of course, the fight is not yet over. The notice also indicates that the FHWA will initiate rulemaking procedures—this time legally, presumably—to repeal the rule. If they do go forward with that proposed action, however, we are ready. As FHWA itself notes, during the initial rulemaking, “Supporting comments came from 91,695 citizens, 9 State DOTs, 24 MPOs, 19 U.S. Senators, 48 Members of the U.S. House of Representatives, over 100 cities, numerous local officials, over 100 businesses, and over 100 public interest, nonprofit and advocacy organizations.” When the time comes, we will once again stand up for this critically necessary rule.

For now we are one step further along the path towards a cleaner, healthier transportation system.